Thermoplastic resins such as styrene resins represented by ABS resins, and alloy materials including styrene resins and other thermoplastic resins are widely used in the fields of, for example, electric and electronic devices, OA and home appliances, vehicles and sanitary products due to their excellent properties such as mechanical characteristics, physical characteristics and electrical characteristics. In association with recent trends such as weight reduction and miniaturization of products, molded articles are reduced in thickness. In the case of, for example, injection molding, thermoplastic resins are subjected to severe conditions such as increased molding temperature and higher injection rate which are necessary in order to obtain thin molded articles. During a molding process with a large molding apparatus, the resin tends to be retained in the cylinder of the molding apparatus and is consequently degraded or thermally decomposed to cause defective molding phenomena such as jetting, and also thermal discoloration. Further, the resulting molded articles are poor in performance and surface appearance.
Thermal stability may be enhanced to a certain extent by adding various thermal stability improvers to thermoplastic resin compositions. This approach, however, increases costs.
Noises and vibrations have become a concern as a result of the recent changes in living environments. There has been a demand that noises and vibrations be reduced in the fields of vehicles, home appliances and OA devices. Materials in need are those capable of reducing vibrations of radiator fans in automobiles, noises from motors in the field of home appliances, and vibrations of optical disks in the field of OA devices.
An example of vibration insulating and vibration damping materials is resin or rubber materials sandwiched between metal plates. The recent weight reduction and miniaturization of devices have made it difficult to adopt such structures in the designing of products, and materials per se which form structures are required to have high vibration damping performance.
In general, highly rigid materials usable as structures by themselves have low vibration damping properties, while materials with high vibration damping properties are poor in rigidity. Because of this trade-off relationship, it is difficult to use resin compositions having vibration damping performance to form structures as such.
Japanese Patent Publication H6-41443A presents a combination of a thermoplastic resin with a copolymer which includes an acrylate ester monomer and/or a methacrylate ester monomer, and a comonomer and which has a glass transition temperature of not less than 0° C. Japanese Patent Publication H11-349785A proposes that a rubbery polymer having a specific core-shell structure is added to a styrene resin. These resin compositions are incapable of giving molded articles with excellent molding processability and excellent surface appearance while still ensuring vibration damping properties.
Japanese Patent Publication 2000-212373A presents a thermoplastic resin composition including a (meth)acrylate ester copolymer and an additional copolymer wherein the thermoplastic resin composition has a loss tangent (tan δ) peak in a specific temperature range different from the Tg peaks of the respective polymers constituting the composition. While this resin composition attains enhancements in molding processability and surface appearance, no effects are obtained in terms of the resistance of the resin composition to thermal discoloration.
Patent Literature 1: Japanese Patent Publication H6-41443A
Patent Literature 2: Japanese Patent Publication H11-349785A
Patent Literature 3: Japanese Patent Publication 2000-212373A